BLOG LINKS for WOOD and WOOD FINISHING

Post 582 –by Gautam Shah

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These are few links on Wood and Wood Finishing processes and materials. Categories covered are:

● WOOD-TIMBER

● WOOD FINISHING

● WOOD COATINGS

● PAINTS-THINNERS

● COMPOSITES

Sawn Timber > Wikipedia image by Kotivalo

 WOOD-TIMBER

WOOD RESOURCES Blog Post 217 Dt 14 Oct 2014

SOFTWOODS and HARDWOODS Blog Post 513 Dt 8 Sept 2015

WOOD COMPOSITES Blog Post 378 Dt 28 March 2015

ROSEWOOD Blog Post 376 Dt 26 March 2015

SOME VARIETIES of WOODS of Indian subcontinent Post 126 Dt 12 July 2015

WOOD-BASED PRODUCTS Blog Post 177 Dt 7 Sept 2014

Finishing a kokeshi in Japan >Wikipedia image by Fg2

WOOD FINISHING

WOOD SURFACE FINISHING Blog Post 472 Dt 13 July 2015

WOOD FINISHES Blog Post 306 Dt 15 Jan 2015

WOOD FINISHES- Dt 22 July 2014

NATURAL OBJECTS and SELF FINISHES Dt 1 Aug 2014

SURFACE FINISHING PROCESSES Blog Post 504 Dt 24 Aug 2015

SURFACE LEVELLING Blog Post 291 Dt 31 Dec 2014

WHAT ONE CAN DO TO A MATERIAL ? Blog Post 334 Dt 12 Jan 2015

JOINTS in SURFACE FINISHES Blog Post 469 Dt 9 July 2015

Japanese Lacquer ware in the Ostasiatiska museet, Stockholm, Sweden >Wikipedia image by Daderot

WOOD COATINGS

WOOD SURFACE PREPARATIONS for CLEAR COATINGS Dt 28 April 2014

CLEAR COATINGS Blog Post 182 Dt 12 Sept 2014

CLEAR COATINGS- Post 119 Dt 4 March 2015

SHELLAC or LAC COATINGS Dt 26 April 2014

UNDERSTANDING LACQUERS Blog Post 498 Dt 16 Aug 2015

LACQUERS or NC LACQUERS Blog Post Dt 27 April 2014

VARNISH Dt 25 April 2014

COATINGS as thin Surfacing Blog Post 482 Dt 25 July 2015

CLEAR versus PIGMENTED COATINGS Blog Post 553 Dt 29 Nov 2015

PRIMER COATINGS Blog Post 442 Dt 7 June 2015

APPLICATION of COATINGS Blog Post 300 Dt 9 Jan 2015

COATINGS -surface finishing technologies Blog Post 238 Dt 8 Nov 2014

FILM FORMING PROCESS in COATINGS Blog Post 173 Dt 3 Sept 2014

SINGLE or MULTI-COAT SYSTEMS Blog Post 437 Dt 30 May 2015

METAL COATINGS Blog Post 438 Dt 1 June 2015

GILDING Blog Post 471 Dt 13 July 2015

Exterior Maple Wood deck staining Flickr image by Olger Fallas

PAINTS-THINNERS

SOLVENTS and THINNERS for coatings Blog Post 320 Dt 29 Jan 2015

PAINT THINNERS – 1 Blog Post 416 Dt 8 May 2015

PAINT THINNERS – Part 2 Blog Post 423 Dt 30 March 2015

SOLVENTS for THINNERS Blog Post 492 Dt 9 Aug 2015

Wood chips composite board > Wikipedia image by C. Sander and durch Urheber

 COMPOSITES

FILLERS and COMPOSITES Blog Post 169 Dt 30 Aug 2014

COMPOSITES – Part 1 Blog Post 156 Dt 17 Aug 2014

INTERFACE OF MATRIX AND FILLER in COMPOSITES Blog Post 180 Dt 10 Sept 2014

MATRIX of COMPOSITES Blog Post 168 Dt 29 Aug 2014

Glue laminated Large span wood beam at Richmond Olympic Oval, > Wikipedia image by Thelastminute (Duncan Rawlinson)

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CLEAR COATINGS

Post 182  –by Gautam Shah 

 

Clear coatings are mainly used to show up the surface grain, colour and pattern. These however, are not always perfect or decent so need to be partially occluded or improvised. Conditioning of the substrate surfaces is needed before the application of a clear coating. The most common problems with surfaces are like:

Clear Coating over wood

• uneven colour
• unsuitable tone
• uneven grain or pattern
• patchy absorbency
• uneven texture
• bleeding or soluble constituents
• waxy or oily deposits
• alkalinity
• acidity
• galvanic sensitivity
• moisture content and transfer
  

  Spectacles lenses have many different types of coatings -scratch proof, colour correction, anti glare / Top without coating + bottom with coating

Such problems with man-made surfaces are controllable at production level, but with natural surfaces like the wood, have to be tackled on the site.

Clear Finishes are also used where for avoidance of pigments with toxicity is required. Food packing, such as of paper, aluminium (cold drink tins), medical bottle stoppers, toys etc. require colourless coatings.

One of the oldest clear coating -wax

For clear coatings, to overcome the surface related problems many types of surface treatments are used. Most surface conditioners or treatments are fast drying, easy to apply, non destructive for the substrate and insoluble in the subsequent coat material.

Surface conditioners are of following types: Fillers (transparent or opaque), levelers, sealers, strainers (soluble and insoluble colourants), printed patterns, patterning tools, etching agents, bleaches, and reactants.

Staining on wood

• Fillers – Sealers are used to fill in pores so that coating material does not sink into it, and provide an even finish. Fillers generally consist of an extender, a binder and occasionally a colourant. Extenders are fine grade powder of materials like gypsum, chalk, china clay, precipitated calcium carbonate, lime, asbestine, colloidal silica, barytes and talc. Binders could be water, gums, oils, alkyds and poly vinyl emulsions. Solvent bound fillers are better compared with water bound fillers, which raise the grain or fibres of the surface. Colourants provide the necessary tint, to white extenders. Fillers, made of pigment powders, serve the purpose of filling as well as staining. Transparent fillers (low body NC lacquer, shellac, etc.) are used, not only to fill the pores, but to provide a sealing-coat to the decayable material in the grains and vessels filled with gum exhudents.
• Stains provide a correct transparent tint to the surface. Stains are generally dye-material soluble in water, oil or solvents. Water soluble stains though of many different varieties raise the fibres and are difficult to penetrate. Oil soluble stains are heavy bodied, take longer to dry out and interfere in the subsequent coating application. Solvent soluble stains are costly, dry out immediately and may bleed residual gums and other exhudents. Stains have one important drawback that they darken the existing colour of the substrate. Where timber surfaces need to be of lighter colour, surfaces have to be bleached or toned with opaque materials.

• Bleaching process include a treatment with hydrogen peroxide followed by an alkaline accelerator like lime, caustic soda, sodium silicate or ammonia. Bleaching affects adhesion and toughness of coating, and it also adds an amber hue to the coating on ageing.
• Imposed patterns: On surfaces where there are very irregular grains, the patterns are screen-printed, pressed or embossed using stains. Such patterns may emulate a wood grain or just very fine mesh or lines. Staining is also done by micro spray guns, singeing, burning or carbon deposition from flames.
• Post application treatments: Clear finishes often require some post application treatments. These are mainly burnishing and waxing. Burnishing is mainly done to NC lacquer, acrylic and melamine coatings to provide a glossy surface. Burnishing is not done to slow drying coatings, because such coatings, though are dry on outer face, take days to thoroughly dry out. Burnishing is done with a Carborundum like rubbing material with a waxy or oily base. Waxing provides a dull sheen and a protective coating. Waxing is also done to renovate old coatings. Waxing compounds also include a small amount of oils and sometime silicone materials.
  

  Anti reflective coating on glass

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WOOD SURFACE PREPARATIONS for CLEAR COATINGS

Post -by Gautam Shah

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Natural Woods are many different types, such as Soft, Medium and Hard grain. Woods are likely to be Fresh, Seasoned and Old woods. Woods have different types of faces such as the end grains, flat and side faces. The woods have problems of uneven colours, patterns. The variations in textures are both natural and tools or machine made.

Wood products have similar problems but an average quality due to the mass production processes. The variations however are between near-natural products (plywoods, veneers) and synthesized products (particle boards, MDFs etc.)

For a clear coating application all wood surfaces require surface preparation treatments and post coating application treatments. The surface preparation treatments are over and above the nominal craft processes such as planing, sand papering, etc. These are mainly Filling, Sealing and Staining. The post coating application treatments are not always required, but could be Buffing, burnishing, waxing, etc.

Fillers

Fillers generally consist of an Extender, a Binder and occasionally a Colourant. Fillers are required to fill in the pores in the wood grains of Natural woods and cavities in case of wood products. A levelled surface provides better gloss and integrity of the coating (one continuous surface without breaks). The coating material does not sink into it, and provide an even finish. Transparent fillers (low body NC lacquer, shellac, etc.) are used not only to fill the pores, but provide a sealing coat to the decayable material in the grains and vessels filled with gum exudates.

Extenders

Extenders are low opacity -reflectivity, fine grade powder of materials like gypsum, chalk, china clay, precipitated calcium carbonate, lime, asbestine, colloidal silica, barytes and talc(unlike the Zinc oxide or Titanium dioxide -the white pigments that adds whiteness and opacity).

Binders

Binders are binding agents that hold together the extenders, temporarily or permanently, and also bind the extenders to the wood substrate. A binder could be water, gums, oils, alkyds and poly vinyl emulsions. Solvent bound binders are better compared to water bound binders. The later ones raise the grain or fibres off the surface.

Colourants

Colourants provide an equalizing tint to the wood surface and slightly colour the white extenders. Fillers, made of low opacity-reflectivity pigments serve a dual purpose, of filling as well as staining.

Stains as colourants

Stains provide a correct transparent tinge to the surface. Stains are generally dye-material soluble in water, oil or solvents. Water soluble stains though of many different varieties, raise the fibres and are difficult to penetrate. Oil soluble stains are heavy bodied, take longer to dry out and interfere in the subsequent coating application. Solvent soluble stains are costly, dry out immediately and may bleed residual gums and other exudates.

Stains have one important drawback that they darken the existing colour of the substrate. Where timber surfaces need to be of lighter colour, surfaces have to be bleached or toned with opaque materials.

Bleaching

Bleaching process lightens the existing colour of the wood. It includes a treatment with hydrogen peroxide followed by an alkaline accelerator like lime, caustic soda, sodium silicate or ammonia. Bleaching affects adhesion and toughness of coating. It also provides an amber hue to the coating on aging. Staining is also done by micro spray guns, singeing, burning or carbon deposition from flames.

Imposed patterns

On wood surfaces where there are very irregular grains or no patterns, these are screen-printed, pressed or embossed using stains. Such patterns may emulate a wood grain pattern or just very fine mesh or lines.

Post application treatments

Clear finishes often require some post application treatments. These are mainly burnishing and waxing. Burnishing is mainly done to NC lacquer, Acrylic and Melamine coatings, to provide a glossy surface. Burnishing is not done to slow drying coatings, because such coatings, though are dry on outer face, take days to thoroughly dry out. Burnishing is done with a Carborundum like rubbing material with a waxy or oily base. Waxing provides a dull sheen and a protective coating. Waxing is also done to renovate old coatings. Waxing compounds also include a small amount of oils and sometime silicone materials.

 

LACQUERS or NC LACQUERS

Post–by Gautam Shah

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Lacquer is a very generic term applied to a variety of coating systems. It indicates a surfacing system, where a film forming substance has been dissolved in or diluted with a solvent. On application the solvent evaporates leaving a thin film on the surface.

The lacquer, on evaporation of its solvents changes the phase from Liquid to Solid, but does not convert itself into different substance. Lacquer films are soluble in the (original) solvent. Lacquers are also thermoplastic (will soften with an increase in heat) materials. The film forming substances of lacquers are linear polymers high in polymer weight with good solvent releasing property. Such substances are often very hard and brittle, so require addition of plasticizers to achieve better adhesion, flexibility and durability of the gloss.

Commercially the term Lacquer is applied to Solvent-based Coating systems (against water-based systems) that offer hard, glossy and durable film. In this sense, there are Two basic varieties:

1 Thermoplastics type: Nitro cellulose, Acrylics, Chlorinated Rubber, Vinyls, Epoxy.

2 Thermosetting type: Acrylics, Epoxy Resins, Polyurethanes, Vinyls, Alkyd, Melamine.

Cellulosic Polymers

Cellulose is the most widely occurring, a natural polymer, available in almost all plants. Primary sources of industrial cellulose are cotton fibres and wood. Cellulose is a polyhydric-alcohol, and forms esters with organic acids. It also forms reaction products with inorganic acids. These cellulosic derivatives used in production of various types of lacquers are classified as:

1. esters of inorganic acids -nitro cellulose

2. esters of organic acids -cellulose acetate

3. others -methyl and ethyl cellulose

Lacquers can be classified into two basic groups:

NC Lacquers and Acrylic or Plastic Lacquers.

Nitro Cellulose Lacquers

NC Lacquers consist of Nitro cellulose as the main raw material to which a variety of plasticizer and resins are added, to provide wide range of film properties. PLASTICIZERS increase elasticity and extensibility of the film. Commonly used Plasticizers are, blown-castor oil, dibutyl phthalate, dioctyl phthalate, dibutyl sebacate, butyl stearate, chlorinated diphenyls. Additions of RESINS increase gloss and adhesion of the film. The resins are coconut and castor oil alkyds, maleic modified ester gum, cyclohexanone (ketonic) resins, acrylic resins, toluene sulfonamides formaldehyde resins.

NC Lacquers are produced by dissolving or diluting lacquer and suitable plasticizers in a mix of solvents. The SOLVENTS act in three ways: Active solvents are (ethyl acetate, butyl acetate), Latent solvents (ethyl alcohol, butyl alcohol, diacetone alcohol), and Dilutents (toluene, xylene). A suitable mix of these basic three types of solvents is known as `Thinner‘. A very specific quality of Thinner is required for each application and weather condition.

NC Lacquers do not become yellow with ageing. It has no peeling problem. Lacquers provide very ‘water-white’ (no colouration or tinge) film. NC Lacquers are re-coatable and removable substances.

NC Lacquers are used on wood, metals, metals like gold, silver and copper, plastics, leather, paper, fabrics, as hair-fixers, and Nail-polishes. Lacquer is one of the best surface sealing material for wood products and so forms the primer coat for melamine, etc. 

Solvent-based nitrocellulose lacquers (from resin of nitration of cotton (lint) and other cellulose based materials, were used commercially from the 19th C. These lacquers began to replace shellac lacquer and were used as protective or rust inhibitive clear coatings for brass musical instruments, gift items and furniture. These were also used in white-goods products (refrigerators, irons, cooking tops, etc. and in automobiles. These lasted for several decades till arrival of ‘Polymer based lacquers‘.

These materials are called Lacquers because the film is ‘water-white’. Acrylic lacquers of thermoplastic type are characterized by a transparent water white film, very good resistance to decolouration from temperature and UV light, good electrical properties, outdoor durability, excellent resistance to mineral oil-greases, resistance to chemical fumes, resistance to water based alkaline substances.

Acrylic lacquers convertible coating that is on drying covert to a different product, which is non-dissoluble and non-removable. These are used for: wood items, clear coating for brass, copper, and aluminium, as a top coat for final gloss and protection air-crafts, automobiles, toys, auto-parts, industrial components, consumer durables, TV cabinets. These are used as clear-invisible coating for exposed surfaces like bricks, stones and concrete. Acrylic lacquers with soluble dyes form transparent glass coatings. One of the major uses is for internal coatings of food and beverage cans.

Thermosetting Acrylics provide a hard and scratch proof coating, good colour retention, better water and detergent resistance, better gloss and chalking resistance.

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SHELLAC COATINGS and FRENCH POLISHES

-Post by Gautam Shah

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SHELLAC or LAC COATINGS

Shellacs Finishes, were the first true clear coatings. It is believed that Shellac is in use for the past 2000 years. It was used as gum, sealing compound, and as a mastic compound.

Shellac is an insect exudate known as stick-lac. It is refined to remove impurities including waxy substances, and lighten its colour. Button-Lac is a manually purified form and is of darker colour, while machine purified shellac is often de-waxed and de-colourized.

Shellac is soluble in methylated spirit or alcohols. It is a very effective coating material even in very thin viscosity, as a result its penetration and filling capacity is excellent. It is one of the best surface filler material. It is eminently re-coat-able so a very smooth level and glossy surface is possible.

Sankheda furniture (Sankheda near Vadodara, Gujarat, India ) and Chinese lacquer items are examples of shellac coatings.

http://gaatha.com/wp-content/uploads/2013/05/Sankheda-furniture-gujarat

FRENCH POLISH

French Polish has been one of the most popular clear (colourless) coating material. It has been used as wood furniture polish, Protective and glossy coating for oil paintings, besides employed as a paper coating, hair fixer, and as a gum for Gold leaf fixing. French Polish is most preferred conservation coating for old furniture and oil paintings. French Polish on drying does not convert into a non-soluble product. It is technically a non-convertible’ coating system. Once applied it can be removed with alcohol like solvent, without damaging the original surface.

French polish is very similar to natural shellac polish. However resistance to wear and tear is poor, and the film is permeable. But it is re-coat-able material.

French polish includes a number of materials that provide a transparent coating. In the past the most important materials were a shellac, and gum copal. But now a days various pine resins, especially maleic modified rosins of spirit soluble type are used.

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VARNISH

Post –by Gautam Shah

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Varnish is clear coating of resin and solvent that dries-hardens to transparent film. Today, Varnish is a generic term for Clear Coatings that provide a colourless (transparent) and (mostly) a glossy surface.

Clear Coatings are required for several reasons, such as to show-up the surface grain, colour, pattern, or protect artwork or craft pieces. The surface to be coated may not always be perfect or decent. So some form of Conditioning of the substrate surfaces is needed before application of a clear coating.

The most common problems with surfaces are like:

1.     uneven colour

2.     unsuitable tone

3.     uneven grain or pattern

4.     patchy absorbency

5.     uneven texture

6.     bleeding or soluble constituents

7.     waxy or oily deposits

8.     alkalinity

9.     acidity

10.   galvanic sensitivity

11.   moisture content and transfer

The word ‘varnish’ comes from Latin ‘vernix’, meaning an odorous resin, Varnish as word comes from Greek ‘Berenice’, which was the ancient name of modern Benghazi in Libya. Perhaps the first varnishes were produced from resins of local trees of Benghazi.

Varnishes are clear coatings usually made with oils, oleo-resinous substances and alkyds. Varnishes are comparatively slow drying, high bodied finishes and so can be applied by brush, unlike Lacquer or French polish. Varnish types of finishes have thicker film of high gloss, with better wear and tear resistance.

Varnishes are convertible coatings (materials, which after application change into different but permanent substance), so are more stable.

In the past varnishes were made by boiling linseed or tung oil with modified rosins. Later varnishes were produced from oils with maleic or phenolic modified resins. Nowadays air drying varnishes (oxidation & polymerization) are produced from long oil alkyds, where as baking varnishes (heat polymerization) are produced from medium or short oil alkyds. Often amino resins such as urea and melamine formaldehyde are added to produce a very tough, hard wearing, solvent insoluble, alkali resistant, non yellowing and non degrading film.

High temperature baking varnishes though superior in many respects have limited use so far as wood, paper and such other surfaces are concerned. Theoretically any film forming medium (used for manufacturing paints -coloured coatings) can be used as a clear coating material, but certain film peculiarities and clarity restrict their use. High grade clear coatings could be of polyurethane, epoxy, polyester, PVA, materials. Varnishes besides wood, are used on paper, leather, fabrics, copper winding wires, pottery products, polymers, insides of food tin and aluminium cans, glass, electronic circuit boards, toys etc.

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